The IP Multimedia Subsystem (IMS) is a data network with an open and standardized architecture for converged fixed and mobile communications services. IMS enables service providers to expand their offerings to their customers by integrating voice and multimedia communications, such as video, text, images and instant messages, and delivering them into new environments. It is well known that IMS is emerging as a viable architecture that potentially may enable the convergence of various forms of communication, including voice and data, fixed and mobile services, public hot spot and enterprise WLAN, into an immersive system to provide the user with a seamless experience across various access networks.
When the IMS standard was originally designed, all subscribers needed to register with the network before they could obtain services from the IMS network. As defined in the 3rd Generation Partnership Project (3GPP) IMS standard, service providers for the IMS network may use the Session Initiation Protocol (SIP) Public User Identity (PUID) as the identifier to recognize the subscriber. SIP is a signaling protocol, widely used for setting up and tearing down multimedia communication sessions such as voice and video calls over the Internet. A PUID enables a network to establish a route to a device that serves the subscriber. An example of information contained in a PUID may include a telephone number or a user@domain. The PUID may be contained in the P-Asserted Identity (PAI) header in SIP INVITE messages and the TO header in SIP registration messages. A SIP INVITE message indicates that the user or service is being invited to participate in a session. The body of the SIP INVITE message includes a description of the session to which the called party is being invited.
Several key issues face service providers who offer services to endpoints via the IMS network. One issue involves the identification records of a calling party. Certain types of endpoints may not have the ability to register with the IMS core network. The calling party identification, such as the originating telephone number and subscriber name, may not be preserved when a call is routed to the IMS network. An endpoint is any user device that is connected to a network. Endpoints can include, for example, a personal computer (PC), a personal digital assistant (PDA), a cellular phone, a landline telephone, a facsimile machine and an aggregate endpoint (AEP). An AEP is an endpoint that has multiple subtending users, but appears as a single SIP User Agent. Examples of aggregate endpoints are IP PBXs, enterprise Voice over Internet Protocol (VoIP) gateways, and IP trunk interfaces to other VoIP networks where end-users on those other networks are not known by the IMS. An AEP may also include customer premises equipment for business wholesale customers. The IMS standard is defined with the concept that a user is registered to the IMS core so that the user can initiate and receive calls from the network. Examples of endpoints that do not have the ability to register with the IMS network includes legacy Time Division Multiplexing (TDM) Private Branch Exchange (PBX) that access an Internet Protocol (IP) network through a VoIP gateway and routers that enable PBX equipment to access to the IMS. Endpoints that do not have the ability to register with the IMS core are referred to as non-registering endpoints (NRE).
Another challenge faced by providers who offer services to aggregate endpoints involves the PAI header. The PAI header, which contains a PUID/calling party number in the IMS network, does not have the same meaning for business and wholesale customers, as is assumed for cellular or consumer customers. Business customers often use the PAI header to signal the call-back number for the business location, but not for the device of the calling party. Wholesale calls typically identify the original calling party number in the PAI header, which identifies the originating caller rather than the wholesale provider who is known to the core service provider's IMS network.